U.S. patent number 6,381,244 [Application Number 09/042,979] was granted by the patent office on 2002-04-30 for connectionless communication method.
This patent grant is currently assigned to Fujitsu Limited. Invention is credited to Hideki Inoue, Takeshi Kimura, Hiroshi Nagano, Takashi Nishimura, Naohide Sekiya, Ikuo Taoka.
United States Patent |
6,381,244 |
Nishimura , et al. |
April 30, 2002 |
Connectionless communication method
Abstract
A plurality of datagram VCCs, each of which is exclusively for
connectionless transfer of data, are established between mutually
adjacent exchanges in advance, one of these datagram VCCs is
assigned exclusively for connectionless data communication and
connectionless communication is performed using this datagram VCC.
Specifically, an originating terminal disassembles connectionless
data into data cells, inserts a cell (a leading cell), which
indicates the destination address of a terminal that is the
destination of the data, at the head of the data cells and then
sends the leading cell to the exchange prior to the data cells. The
exchange assigns a prescribed datagram VCC for connectionless
communication upon referring to the destination terminal address
indicated by the leading cell and thenceforth uses this VCC to
transmit data cells having line identifier identical with that of
the leading cell.
Inventors: |
Nishimura; Takashi (Kawasaki,
JP), Sekiya; Naohide (Kawasaki, JP),
Kimura; Takeshi (Kawasaki, JP), Inoue; Hideki
(Kawasaki, JP), Nagano; Hiroshi (Kawasaki,
JP), Taoka; Ikuo (Kawasaki, JP) |
Assignee: |
Fujitsu Limited (Kawasaki,
JP)
|
Family
ID: |
17713057 |
Appl.
No.: |
09/042,979 |
Filed: |
March 17, 1998 |
Foreign Application Priority Data
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Oct 20, 1997 [JP] |
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9-287099 |
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Current U.S.
Class: |
370/395.21;
370/395.31; 370/395.51 |
Current CPC
Class: |
H04L
12/5601 (20130101); H04L 2012/562 (20130101); H04L
2012/5645 (20130101) |
Current International
Class: |
H04L
12/56 (20060101); H04L 012/56 () |
Field of
Search: |
;370/395,396,397,398,399,400,409,410,422,426,473,474,395.1,395.2,395.21,395.3 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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4230142 |
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Aug 1992 |
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JP |
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4138739 |
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May 1998 |
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JP |
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Primary Examiner: Yao; Kwang B.
Attorney, Agent or Firm: Rosenman & Colin LLP
Claims
What is claimed is:
1. A connectionless communication method for connectionless
transmission of data, comprising the steps of:
establishing a plurality of virtual channel connections, each of
which is exclusively for connectionless transfer of data, between
mutually adjacent exchanges beforehand;
disassembling connectionless data into data cells in a
terminal;
inserting a leading cell, which indicates a destination terminal
address of a terminal that is the destination of the data, at the
head of the data cells and making a line identifier of the leading
cell identical with line identifiers of the data cells in the
terminal;
sending the leading cell from the terminal to an exchange prior to
the data cells;
in the exchange, assigning a prescribed virtual channel connection
exclusively for communication of said connectionless data upon
referring to the destination terminal address contained in the
leading cell;
transmitting data cells, which have the line identifier identical
with that of the leading cell, from the exchange toward the
destination terminal, using the virtual channel connection that has
been assigned;
storing correspondence between the line identifier of the leading
cell and the line identifier of the assigned virtual channel
connection in a switching table which is provided in the
exchange;
inserting, into the leading cell, data indicating a necessary
bandwidth or necessary quality of communication class required for
connectionless communication;
providing an exchange with a virtual channel connection table for
managing the virtual channel connections set in advance for
connectionless communication; and
in the exchange, managing through use of the virtual channel
connection table, in-use/not-in-use state of each virtual channel
connection and bandwidths or quality of service classes set for the
virtual channel connections, referring to the virtual channel
connection table to select a virtual channel connection optimum for
the necessary bandwidth or necessary quality of service class
indicated by the leading cell, and assigning this virtual channel
connection for connectionless communication,
wherein the exchange refers to the switching table to transmit,
using the assigned virtual channel connection, data cells having
the line identifier identical with that of the leading cell.
2. The method according to claim 1, wherein in a case where the
terminal performs connection-oriented communication, the terminal
sends a signaling cell to request establishment of a connection,
attaches line identifier, which has been specified in response to
the request, to data cells and sends the data cells; and
in a case where the terminal performs connectionless communication,
the terminal attaches line identifier of a virtual channel
connection, which has been established between the terminal and an
exchange beforehand, to the leading cell and sends the leading cell
to the exchange, thereafter attaches the same line identifier as
the abovementioned line identifier to the data cells and sends the
data cells to the exchange.
3. The method according to claim 1, wherein the leading cell has an
identifier which indicates that the cell is the leading cell, and
the exchange identifies the leading cell by this identifier.
4. The method according to claim 1, wherein the leading cell has a
protocol identifier for identifying which protocol address is
specified by a destination terminal address; and
the exchange refers to the protocol identifier to judge which
protocol address is specified by the terminal address indicated by
the leading cell.
5. The method according to claim 1, further comprising the
following steps in a case where a virtual channel connection that
satisfies the necessary band or necessary quality of service class
required by the terminal does not exist:
causing the exchange to start communication upon temporarily
assigning a virtual channel connection that does not satisfy the
necessary band or necessary quality of service class; and
causing the exchange to raise, while communication is in progress,
a set bandwidth or quality of service class of this assigned
virtual channel connection to the necessary bandwidth or necessary
quality of service class required by the terminal.
6. The method according to claim 5, further comprising the
following step in a case where a physical line in which the
temporarily assigned virtual channel connection exists does not
possess enough surplus bandwidth to raise the set bandwidth of the
virtual channel connection to the necessary bandwidth:
causing the exchange to determine whether an unused virtual channel
connection exists in this physical line and, if such a virtual
channel connection exists, to reduce the set bandwidth of the
unused virtual channel connection and increase the set bandwidth of
the temporarily assigned virtual channel, connection.
7. The method according to claim 5, further comprising the
following steps of:
in a case where a physical line in which an assigned virtual
channel connection exists does not possess enough surplus bandwidth
to increase the set bandwidth of the virtual channel connection,
sending a request for establishment of a direct virtual channel
connection between an originating terminal and a destination
terminal, from the exchange to a network management center; and
executing communication between the terminals via a direct route
different from a route based upon the ready assigned virtual
channel connection.
8. The method according to claim 7, wherein the exchange is
provided with a virtual channel connection establishing agent, said
virtual channel connection establishing agent generates signaling
data upon referring to the necessary bandwidth required by the
terminal, entered in the virtual channel connection table, sends
the signaling data to the network management center and requests,
instead of the terminal, establishment of a direct virtual channel
connection between the terminals.
9. The method according to claim 7, wherein when the originating
terminal has received line identifier of a direct virtual channel
connection from the network management center, the terminal
attaches these line identifier to cells, sends the cells to the
exchange and notifies the exchange, by a communication-end
notification cell, of end of communication based upon the virtual
channel connection allocated thus far.
10. The method according to claim 7, wherein the exchange that has
sent the network communication center the request for establishing
a direct virtual channel connection is made an exchange directly
accommodating the originating terminal, and an exchange located
along a route sends the exchange directly accommodating the
originating terminal a bandwidth deficiency notification cell
indicative of insufficient bandwidth.
11. The method according to claim 1, further comprising the
following step of:
when the necessary bandwidth or necessary quality of service class
has changed during communication using the assigned virtual channel
connection, sending a request-change cell to the exchange from the
terminal to notify the exchange of the change in necessary
bandwidth or necessary quality of service class.
12. The method according to claim 11, further comprising the
following steps of:
when the exchange has received a leading cell or a request-change
cell from the terminal, distinguishing between the leading cell and
the request-change cell by verifying whether line identifiers of
the cell have been stored in the switching table; and
in a case where the request-change cell has been received,
refraining from executing routing processing and executing
processing for changing the set bandwidth of an already assigned
virtual channel connection to the necessary bandwidth.
13. The method according to claim 1, further comprising the steps
of:
sending a communication-end notification cell from the terminal to
the exchange when connectionless communication has ended; and
causing the exchange to restore the assigned virtual channel
connection to a not-in-use state in response to receipt of the
communication-end notification cell.
14. The method according to claim 1, further comprising the steps
of:
inserting data, which is indicative of persistence of
communication, in the leading cell;
managing persistence of communication of each virtual channel
connection by the virtual channel connection table and, if the
persistence of communication of a prescribed virtual channel
connection exceeds a threshold value, causing the exchange to
request a network management center to establish a direct virtual
channel connection between an originating terminal and a
destination terminal; and
executing communication between the terminals via a direct route
different from a route based upon the already assigned virtual
channel connection,.
15. The method according to claim 1, further comprising a step of
continuously sending leading cells, the number of which is
equivalent to the number of destination terminals of other parties,
from an originating terminal in a case where multicast
communication is performed.
16. The method according to claim 1, further comprising the steps
of:
continuously sending leading cells, the number of which is
equivalent to the number of destination terminals of other parties,
from an originating terminal in a case where multicast
communication is performed;
causing the exchange, which has received a leading cell, to obtain
a switching destination by referring to a destination terminal
address that has been inserted into the leading cell, to judge
whether the switching destination has duplicated a prevailing
multicast switching destination and, if the switching destination
is not duplicated, to assign a prescribed virtual channel
connection; and
registering correspondence between the line identifier of the
leading cell and the line identifier of the assigned virtual
channel connection in a switching table.
Description
BACKGROUND OF THE INVENTION
This invention relates to a connectionless communication method for
the connectionless transmission of user data. More particularly,
the invention relates to a datagram-type connectionless
communication method in which a cell (also referred to as a
"leading cell" below) which includes the address of a destination
terminal and the like is inserted at the head of a cell stream
transferred with an attached prescribed line identifier, and the
network transmits a user cell to the destination terminal upon
referring to the leading cell.
(a) Connection-oriented Communication and Connectionless
Communication
There are two methods of connecting terminals, namely a
connection-oriented method and a connectionless method. As shown in
FIG. 31A, the connection-oriented communication method involves
dialing a number, for example, verifying the transmitting side (A
system) and receiving side (B system) prior to the start of
communication so as to ring the other party's bell, establishing a
path between the two sides and then performing data communication
via the established path. This method is advantageous in that
reliable communication is possible via a connected line and in that
it is simple to transfer information after the connection is
established. However, since making the connection takes time, this
method is not efficient for the transmission of data of short
duration.
The connectionless communication method, on the other hand, as
shown in FIG. 31B, involves collecting transmission data into
packets, attaching destinations to the packets and then sending the
packets to a network, whereupon the network checks the destination
of each packet one by one and transmits each packet to the
destination terminal. Since making a connection with this method
does not take time, even short-duration data can be sent
efficiently.
In order to make possible multimedia transmission which includes
the transmission of video, ATM (Asynchronous Transfer Mode)
technology has been developed in association B-ISDNs and a variety
of communication services have been realized. A B-ISDN is capable
of providing both connection-oriented and connectionless
services.
(b) Connection-oriented Communication in ATM Networks
FIG. 32 is a diagram useful in describing connectionless
communication in an ATM network. Shown in FIG. 32 are ATM terminals
A.about.D, ATM exchanges EX1.about.EX4, a network NWK composed of a
group of ATM exchanges, and a network management center NMC. In a
case where terminal A is to perform connection-oriented
communication with terminal C, the following procedure for
establishing a VCC (Virtual Channel Connection) is required:
(1) Terminal A issues a request for communication with terminal C
to the network management center NMC via a common signal line (a
VCC for signaling).
(2) The network management center NMC responds to the request from
terminal A by performing computation to determine that the VCC
between the terminals A and C via the ATM exchanges EX1, EX2, EX3,
EX4, in the order mentioned, is the most advantageous route, and by
instructing each ATM exchange to establish the VCC.
(3) The ATM exchange EX1 notifies terminal A and the ATM exchange
EX4 notifies terminal C of line identifiers VPI, VCI used in
communication.
(4) Terminal A disassembles data into cells, attaches the line
identifiers of which it has been notified to the cells and then
sends the cells to the line. Each of the exchanges EX1.about.EX4
exchanges and transmits the cells while changing the line
identifiers of the cells. Terminal C accepts the cells, which have
the specified line identifiers, transmitted from the exchange EX4
and assembles the cells into data.
(c) Connectionless Communication in ATM Networks
(c-1) Problem Which Arises When Connectionless Communication is
Used in ATM Networks
The header of an ATM cell contains only virtual line identifiers
such as VCI and VPI. That is, the header does not contain an
address indicating the destination terminal. Consequently,
providing a connectionless communication service such as electronic
mail is accompanied with difficulties. For example, if the average
downloaded file size on the WWW (Worldwide Web) is two kilobytes
and the ATM switch transmits at a rate of 155 megabits per second,
then this is the size of a file that can be downloaded in 100
microseconds. However, since an ATM switch requires 10 milliseconds
to be connected, 99% is the overhead for the connection. In other
words, if an ATM network of the connection-oriented transfer type
is used as a transmission path for implementing a connectionless
communication service, a delay occurs owing to the time needed to
establish the connection.
Solutions to this problem include a PVC (Permanent Virtual Circuit)
in the ATM layer and a datagram in a higher layer (e.g., IP
layer).
(c-2) PVC Technique
The PVC technique involves establishing end-to-end PVCs beforehand
between all of the terminals A.about.F that are capable of
communicating, as shown in FIG. 33. However, this method is
disadvantageous in that PVC resources are wasted. In particular,
this method cannot be employed in a large-scale network (the
Internet, for example) in which communication is performed between
an unspecified number of terminals.
(c-3) Datagram Technique
With the datagram technique, as shown in FIG. 34, PVCs (datagram
VCCs: VCC1.about.VCC7) are established beforehand between the
terminals A.about.F and whichever of the exchanges EX1, EX2 is
nearest to them, and between the mutually adjacent exchanges EX1
and EX2. An IP packet of a higher layer is assembled from ATM cells
by each exchange and switching processing is executed upon
observing the terminating-side terminal address that has been
entered in the IP packet header. It should be noted that a
"datagram" is the unit in which messages are handled in accordance
with the IP (Internet Protocol). A datagram technique is a method
of providing a destination address in the header of a packet,
deciding, on each occasion, the transfer route for each packet and
then transmitting the packet.
FIG. 35 is a diagram showing the relationship between an IP packet
(IP datagram) and ATM cells. Here P represents an IP packet, which
is composed of a header PH and transmission data DT. The header PH
includes a variety of information, such as a source address SA and
destination address DA. The IP packet P is partitioned into a
number of ATM cells CL.sub.1.about.CL.sub.n, and a header HD is
added onto each cell at the beginning thereof. Line identifiers
(VPI/VCI) included in the headers of the cells
CL.sub.1.about.CL.sub.n have identical values.
FIG. 36 is a diagram showing the structure of an exchange which
implements the conventional datagram approach. Shown in FIG. 36 are
an exchange 1, an ATM switch unit 2, and an IP router 3. (1) A
switching able 2a of the ATM switch unit 2 stores the
correspondence between the input line identifiers (input VPI/VCI)
and output line identifiers (output VPI/VCI), and an ATM switch 2b
generally switches a cell, which arrives from the VCC, to a
prescribed route based upon the content of the switching table 2a.
(2) If a cell arrives from a datagram VCC, the ATM switch unit 2b
delivers this cell to the IP router 3. A packet assembler 3a in the
IP router 3 assembles ATM cells into an IP packet and delivers the
IP packet to a routing controller 3c. (3) A routing table 3b stores
the correspondence between terminal addresses and
output-destination datagram VCCs. Accordingly, the routing
controller 3c refers to the routing table 3b to obtain an
output-destination datagram VCC that corresponds to a destination
terminal address indicated by the header of the entered IP packet
and notifies the ATM switch 2b to perform the switching of one
packet.
In this datagram approach involving a higher layer (the IP layer),
it is required that the above-mentioned processing operations (2)
and (3) be performed whenever a cell arrives from the datagram VCC.
An additional problem is that assembling the packet in step (2)
above takes time.
Another problem is that the bandwidth of the line is exceeded or
that the quality of the communication service cannot be assured.
FIG. 37 is a diagram useful in describing this problem. This
illustrates a case in which data is transmitted from terminal A to
terminal E and from terminal B to terminal F by the datagram method
(connectionless communication). An output-destination datagram VCC
(VCC4) has been stored in the routing table 3b of the exchange EX1
in correspondence with the terminal addresses of the
terminating-side terminals E, F, as shown in FIG. 36. Accordingly,
a cell destined for terminal E arriving from the terminal A via the
datagram VCC (VCC1) is sent to the output-destination datagram VCC
(VCC4). Similarly, a cell destined for terminal F arriving from the
terminal B via the datagram VCC (VCC2) is sent to the datagram VCC
(VCC4). Though not shown, all datagram VCCs (VCC4) are allocated to
cells addressed to terminals accommodated by the exchange EX2 from
other terminals accommodated by the exchange EX1. Consequently, the
bandwidth of the line LNG is exceeded or the quality of the
communication service cannot be assured.
More specifically, since the datagram scheme requires IP layer
switching at each exchange, a problem which arises is that the
high-speed capability of the ATM switch cannot be manifested fully.
Further, with the datagram scheme, one datagram VCC (VCC4)
established between the exchanges EX1 and EX2 (FIG. 37) is used
arbitrarily by a plurality of connectionless communication
operations at the same time, as a consequence of which
communication quality and the bandwidth necessary for persistence
of communication cannot be assured. This means that this method is
not suited to communication at a constant bit rate, which requires
a real-time capability.
The cut-through method using an ATM switching unit is available as
a solution to the above-mentioned problem encountered with the
datagram method. FIG. 38A is a diagram useful in describing
cut-through. Shown in FIG. 38A are the exchanges (IP switches)
EX1.about.EX3, the ATM switch unit 2 and the IP router 3.
Ordinarily, an IP packet is assembled from ATM cells that have
arrived via the datagram VCC (shared VCC) and switching is
performed based upon the destination IP address, as described
earlier with reference to FIG. 36. With cut-through, however, a
special-purpose ATM connection (VCC) between terminals A and E is
established between the IP switches EX1, EX2 during the course of
communication, and communication between the terminals A and E is
performed via this VCC. As a result, route selection by the IP
router 3 is made unnecessary and cut-through (a short cut) via the
ATM switch unit 2 is achieved to realize higher speed.
An opportunity to use cut-through is when a terminal sends a packet
required by an RSVP (resource reservation Protocol). The RSVP is a
higher layer protocol than the Internet Protocol and demands
bandwidth necessary for continuation of communication. By adopting
this approach, the IP switch (exchange) is capable of ascertaining
the required bandwidth and establishes the special-purpose VCC
between the terminals A and E at the required bandwidth, thereby
assuring the acquisition of the bandwidth necessary for
continuation of communication. In other words, as shown in FIG.
38B, (1) switching usually is performed via the IP router. (2) When
a packet demanded by the RSVP is detected, the required bandwidth
is verified and the short-cut VCC is established at this
bandwidth.
However, cut-through is merely an attempt to speed-up processing by
the IP switch and assure the necessary bandwidth; it does not
necessarily make possible the efficient utilization of network
resources. For example, even if the IP switch is cut through, the
route is still that decided by the IP router. When viewed from the
end-to-end terminals, this route is not necessarily the shortest.
In addition, in a case where the necessary bandwidth cannot be
acquired with the route decided by the IP router, another route
cannot be selected.
SUMMARY OF THE INVENTION
Accordingly, an object of the present invention is to make possible
high-speed connectionless communication utilizing fully the
high-speed switching characteristics of an exchange, e.g., an ATM
exchange, for connection-oriented communication.
Another object of the present invention is to make possible
datagram-type connectionless communication by inserting a datagram
cell (leading cell), which indicates the address of the destination
terminal, the necessary bandwidth desired by the terminal and the
quality of service, at the head of a cell stream.
Another object of the present invention is to arrange it so that a
network decides the shortest route and acquires the network
resources necessary for persistence of communication and
maintenance of communication quality while communication is being
supported over route that has been decided by the datagram
method.
A further object of the present invention is to arrange it so that
a variety of protocols are handled by making it possible to
identify which protocol address is specified by an address
indicated by a datagram cell (leading cell).
Yet another object of the present invention is to notify a network
of the latest required particulars and carry out communication
conforming to the latest required particulars in a case where the
necessary bandwidth and QOS (Quality of Service) class required by
a terminal are changed during the course of communication.
Still another object of the present invention is to restore an
assigned VCC to a not-in-use state in response to the end of
communication (connectionless communication) based upon the
datagram approach, thereby making it possible to utilize this VCC
again for the purpose of another connectionless communication
operation.
Another object of the present invention is to so arrange it that
when a physical line which includes an assigned VCC does not have
enough surplus bandwidth to satisfy a bandwidth of the same class,
communication which satisfies the necessary bandwidth and QOS
demanded by a terminal can be performed over a direct route
separate from a communication route based upon the datagram
approach.
Another object of the present invention is to so arrange it that
when persistence (duration) of communication is managed and a
datagram VCC for which persistence exceeds a certain threshold
value exists, communication which meets the requirements demanded
by a terminal can be performed over a direct route separate from a
communication route based upon the datagram approach, thereby
preventing lack of standby datagram VCCs in order to perform
communication that continues over an extended period of time.
A further object of the present invention is to avoid duplication
of direct VCC establishment requests to a network management center
by arranging is so that an exchange which issues a direct VCC
establishment request to the network management center is made only
the exchange that accommodates the originating terminal.
A further object of the present invention is to lighten the load
upon the originating terminal and suppress an increase in traffic
in datagram-type multicast communication.
In accordance with the present invention, the foregoing objects are
attained by providing a connectionless communication method for the
connectionless transmission of data, comprising the steps of (1)
establishing a plurality of VCCs (Virtual Channel Connections),
each of which is exclusively for connectionless transfer of data,
between mutually adjacent exchanges beforehand, (2) assigning one
of the VCCs exclusively for connectionless data communication
between terminals, and (3) performing connectionless data
communication using this one VCC.
In accordance with the present invention, the foregoing objects are
attained by providing a connectionless communication method for the
connectionless transmission of data which further comprises the
steps of (4) causing a terminal to disassemble connectionless data
into data cells and then send the data cells, (5) causing the
terminal to insert a cell (leading cell), which indicates a
destination terminal address of a terminal that is the destination
of the data, at the head of the data cells and send the leading
cell prior to the data cells, (6) causing an exchange to assign a
prescribed VCC for communication of the above-mentioned
connectionless data upon referring to the destination terminal
address contained in the leading cell, and (7) causing the exchange
to transmit data cells, which have line identifier identical with
that of the leading cell, using the VCC that has been assigned.
Other features and advantages of the present invention will be
apparent from the following description taken in conjunction with
the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a diagram useful in describing an overview of a
communication system according to the present invention;
FIG. 2 is a diagram useful in describing the relationship between
an IP packet and ATM cells;
FIG. 3 is a diagram showing the configuration of a network which
performs connectionless communication according to the present
invention;
FIG. 4 is a diagram showing the construction of a terminal;
FIG. 5 is a diagram showing the construction of an exchange;
FIG. 6 is a diagram useful in describing the operation of the
exchange;
FIG. 7 is flowchart illustrating the operation of the exchange;
FIGS. 8A and 8B are diagrams useful in describing the content of
tables;
FIG. 9 is a diagram showing the construction of an exchange
equipped with a function for optimizing allocated bandwidth;
FIG. 10 is a flowchart showing control for optimizing allocated
bandwidth;
FIGS. 11A, 11B and 11C are diagrams useful in describing the
content of a VCC table;
FIG. 12 is a diagram useful in describing the operation of ATM
terminal when a request is changed;
FIG. 13 is a flowchart showing control performed by an exchange
when a request is changed;
FIG. 14 is a flowchart of optimization processing executed by
exchange;
FIGS. 15A and 15B are diagrams useful in describing the operation
of the ATM terminal when communication ends;
FIG. 16 is a flowchart of communication termination processing
executed by an exchange;
FIGS. 17A and 17B are diagrams useful in describing the content of
various tables;
FIG. 18 is a diagram showing the configuration of a network that
makes possible control for establishing a direct VCC;
FIG. 19 is a diagram showing the construction of an exchange
equipped with a VCC establishing function;
FIG. 20 is a flowchart of processing for establishing a direct VCC
and for performing communication control (for increasing
bandwidth);
FIG. 21 is a diagram useful in describing communication control of
a terminal based upon a direct VCC;
FIG. 22 is a flowchart of processing for establishing a direct VCC
and for performing communication control (for increasing
communication persistence);
FIG. 23A is a diagram showing the configuration of a network useful
in describing control for requesting establishment of a VCC, and
FIG. 23B is a diagram useful in describing the structure of cell
which notifies of inadequate bandwidth;
FIG. 24 is a flowchart of processing executed by an exchange to
request establishment of a VCC;
FIGS. 25A and 25B are diagrams useful in describing multicast
communication;
FIG. 26 is a diagram useful in describing control for specifying
the terminals of parties involved in multicast communication;
FIGS. 27A, 27, and 27C are diagrams useful in describing the
content of switching tables;
FIGS. 28A, 28B and 28C are diagrams useful in describing the
content of a VCC table of datagram VCCs addressed from exchange EX1
to exchange EX2;
FIG. 29 is the first part of a flowchart of exchange control
inclusive of multicast processing;
FIG. 30 is the second art of the flowchart of exchange control
inclusive of multicast processing;
FIGS. 31A and 31B are diagrams useful in describing
connection-oriented communication and connectionless communication
according to the prior art;
FIG. 32 is a diagram useful in describing connection-oriented
communication;
FIG. 33 is a diagram useful in describing the PVC technique
according to the prior art;
FIG. 34 is a diagram useful in describing the datagram technique
according to the prior art;
FIG. 35 is a diagram showing the relationship between an IP packet
and ATM cells according to the prior art;
FIG. 36 is a diagram showing the construction of an exchange which
implements the conventional datagram method;
FIG. 37 is a diagram useful in describing a conventional method in
a case where data is communicated from a terminal A to a terminal E
and from a terminal B to a terminal F; and
FIGS. 38A and 38B are diagrams useful in describing a
short-cut.
DESCRIPTION OF THE PREFERRED EMBODIMENT
(A) Principle of the Present Invention
FIGS. 1 and 2 are diagrams useful in describing the principle of
the present invention, in which FIG. 1 is an overview of a
communication system and FIG. 2 illustrates the relationship
between an IP packet and ATM cells.
Shown in FIG. 1 are terminals A, B, C, D and ATM exchanges EX1 and
EX2. Further, VCC1 is a datagram VCC between the terminal A and the
exchange EX1, VCC2 a datagram VCC between the terminal B and the
exchange EX1, VCC3 and VCC4 datagram VCCs between the exchanges EX1
and EX2, VCC5 a datagram VCC between the terminal C and the
exchange EX2, and VCC6 a datagram VCC between the terminal D and
the exchange EX2. Further, ST represents a switching table storing
data which decides the switching paths of cells, and VT represents
a VCC table which manages datagram VCCs.
An IP packet 1001 and an ATM cell group 1002 are shown in FIG. 2.
The IP packet 1001 is composed of a header PH and transmission data
DT. The header PH includes a variety of information, such as a
source address SA and destination address DA (see FIG. 35). The IP
packet 1001 is partitioned into a number of ATM cells
CL.sub.1.about.CL.sub.n, and an ATM header HD is added onto each
cell. A datagram cell (also referred to as a "leading cell")
C.sub.0, in which the address of the destination terminal has been
entered, is inserted at the head of the ATM cells
CL.sub.1.about.CL.sub.n. The payload of the leading cell has (1) a
field F1 in which a 2-bit cell identifier ID, which indicates that
the cell is a datagram cell, is entered, (2) a field F2 in which a
destination terminal address DA is entered, (3) a field F3 in which
an originating terminal (source terminal) address SA is entered,
and (4) a field F4 in which a protocol identifier, traffic
descriptor (necessary bandwidth), quality of service (QOS) and
communication persistence, are entered.
(a) A plurality of VCCs [datagram VCCs (VCC3, VCC4)], which are
exclusively for connectionless transfer of data, are established
between the exchanges EX1 and EX2 in advance, one datagram VCC is
assigned to connectionless data communication, and connectionless
data communication is performed using this datagram VCC. More
specifically, in a case where the originating terminal A transmits
data to the terminal C, the connectionless data (IP packet 1001) is
disassembled into the cells C.sub.1.about.C.sub.n, the cells
C.sub.1.about.C.sub.n are sent to the datagram VCC (VCC1), and the
datagram cell (leading cell) C.sub.0, which indicates the address
of the cell C that is the destination of the data, is sent to the
exchange EX1 upon being inserted at the head of the cells
C.sub.1.about.C.sub.n. The exchange EX1 refers to the destination
terminal address indicated by the leading cell C.sub.0, assigns a
prescribed output-side datagram VCC (VCC3) for connectionless
communication of the data and thenceforth transmits the data cells
C.sub.1.about.C.sub.n, which have line identifiers (VPI/VCI)
identical with those of the leading cell, via the datagram VCC
(VCC3). In this case the exchange EX1 stores the correspondence
between line identifiers of the leading cell C.sub.0 and the line
identifiers of the datagram VCC (VCC3) in the switching table ST,
refers to the switching table and transmits the data cells
C.sub.1.about.C.sub.n, which have line identifiers identical with
those of the leading cell C.sub.0, via the datagram VCC (VCC3) that
has been assigned. Similarly, the exchange EX1 assigns a datagram
VCC (VCC4) for connectionless communication of data from the
originating terminal B to the terminal D.
If this arrangement is adopted, exchanges for connection-oriented
communication, e.g., the ATM exchanges EX1 and EX2, need not
assemble ATM cells into an IP packet, thus making possible
connectionless communication in which the high-speed switching
characteristic of the ATM exchanges is exploited fully. Further,
since a plurality of datagram VCCs are provided between the
exchanges, communication can be carried out by assigning a single
prescribed datagram VCC for each connectionless communication
operation. This makes possible connectionless communication that
meets the bandwidth and QOS requirements of the terminal.
(b) A protocol identifier, which identifies which protocol address
is specified by a destination terminal address, is included in the
leading cell C.sub.0, whereby each of the exchanges EX1, EX2 is
capable of identifying, by referring to the protocol identifier,
which protocol address is specified by the terminal address
indicated by the leading cell C.sub.0. If this arrangement is
adopted, not only the Internet Protocol but various other higher
layer protocols can be supported.
(c) Data indicating bandwidth or quality of service class (QOS
class) required for connectionless communication is included in the
leading cell C.sub.0, and the exchanges EX1, EX2 are made to
manage, by a VCC table VT, in-use/not-in-use state of each datagram
VCC and bandwidths or QOS classes set for datagram VCCs. If this
arrangement is adopted, the exchanges EX1, EX2 can, by referring to
the VCC table VT, assign a datagram VCC having the necessary
bandwidth or QOS class indicated by the leading cell.
(d) In a case where a datagram VCC that satisfies the necessary
bandwidth or QOS class requested by an originating terminal does
not exist between the exchange EX1 and the exchange EX2, the
exchange EX1 starts communication by temporarily assigning a
datagram VCC that does not satisfy the necessary bandwidth or QOS
class. Then, during the course of communication, the exchange EX1
raises the set bandwidth or QOS class of the assigned VCC up to the
bandwidth or QOS class required by the terminal. If the physical
line over which the assigned datagram VCC exists does not have
enough surplus bandwidth to attain the necessary bandwidth in this
case, the exchange EX1 checks to determine whether an unused
datagram VCC exists in this line. If such a datagram VCC exists,
then the exchange EX1 reduces the set bandwidth of the unused VCC
to obtain the necessary bandwidth. If this arrangement is adopted,
communication can be started immediately even in a case where a
datagram VCC that satisfies the necessary bandwidth or QOS class
demanded by a terminal does not exist. Moreover, communication
which meets the needs of the terminal can be performed after the
start of communication.
(e) When the necessary bandwidth or QOS class changes during
communication using an assigned datagram VCC, the terminal
transmits a datagram cell (a request-change cell) to the exchange
in order to notify the exchange of the change in necessary
bandwidth or QOS class. Upon receiving the request-change cell, the
exchange, rather than executing routing processing, executes only
processing for altering the set bandwidth of the already assigned
datagram VCC to the necessary bandwidth. If this arrangement is
adopted, the exchange is freed from execution of routing
processing, as a result of which the load is reduced. Moreover,
communication that satisfies requirements after a change can be
performed.
(f) When connectionless communication using a datagram VCC ends,
the terminal sends the exchange a datagram cell (communication-end
notification cell) indicative of end of communication, and the
exchange responds to the communication-end notification cell by
restoring the assigned datagram VCC to a not-in-use state. As a
result, a datagram VCC can be utilized again for another
connectionless communication.
(g) When the necessary bandwidth or QOS class changes during
communication using an assigned datagram VCC and the physical line
that includes this datagram VCC does not have enough surplus
bandwidth to increase the set bandwidth to the necessary bandwidth,
the exchange requests the network management center to establish a
direct VCC between terminals and causes execution of communication
between the terminals via a direct route that differs from the
route based upon the already assigned datagram VCC. This makes
possible communication that positively satisfies requirements after
a change.
(h) Data indicative of communication persistence is included in a
leading cell and an exchange manages communication persistence of
each datagram VCC by a VCC table. If communication persistence
exceeds a predetermined threshold value, the exchange requests the
network management center for establishment of a direct VCC between
terminals and causes execution of communication between the
terminals via a direct route that differs from the route based upon
the already assigned datagram VCC. If this expedient is adopted, it
is possible to prevent lack of standby datagram VCCs in order to
perform communication that continues over an extended period of
time.
(i) An exchange which sends the network management center a request
to establish a direct VCC is made the exchange directly
accommodating the originating terminal. An exchange located along
the route sends the exchange directly accommodating the
above-mentioned originating terminal a bandwidth deficiency
notification cell indicative of insufficient bandwidth. As a result
of this arrangement, only one exchange requests the network
management center to establish a direct VCC, thus making it
possible to avoid duplication of direct VCC establishment
requests.
(j) In case of multicast communication, an originating terminal
continuously transmits leading cells the number of which is
equivalent to the number of terminals of the other parties. Upon
receiving a leading cell, an exchange determines the destination
switch by referring to the destination terminal address indicated
by the leading cell. If this switching destination does not
duplicate the prevailing switching destination, then the exchange
assigns a prescribed VCC and registers the correspondence between
the line identifiers of the leading cell and the line identifiers
of the assigned VCC in the switching table. As a result of this
arrangement, cells are sent via a common path up to a branch point
and the cells are copied at the branch point and then distributed
to the destination terminals. This lightens terminal load and
suppresses an increase in traffic in multicast communication.
(B) Overview of the Present Invention
(a) ATM-based Datagram Service
In the prior-art example of communication using the datagram
technique, switching cannot be performed in the ATM layer and is
required to be performed in the higher IP layer. The reason is as
follows: The line identifiers VPI and VCI for the switching of an
ATM cell are assigned on a per-VCC basis when the VCC (connection)
is established. With the datagram approach (connectionless
communication approach), therefore, in which no VCC is established,
a certain single VPI, VCI is shared in any communication between
terminals. Consequently, according to the datagram service, the
destination to which an ATM cell is to be transferred cannot be
judged merely by scrutinizing the line identifiers (VPI/VCI) that
have been entered in the ATM header of the cell. Accordingly, with
the datagram service, it is necessary to decide the transfer
destination by reassembling the ATM cells into an IP packet and
reading the IP address of its destination terminal.
In order to perform IP layer switching, however, the ATM cells must
be reassembled into an IP packet and the reassembly takes
considerable time. This makes it impossible to manifest the
capability of ATM switches.
Accordingly, with the connectionless communication method of the
present invention, the arrangement is such that when an originating
terminal starts sending data to another party's terminal in the
form of ATM cells, the datagram cell (leading cell) C.sub.0
indicating the address (IP address) of the destination terminal is
attached to the head of the cell stream, as shown in FIG. 2, and
the cell stream and leading cell are sent to the exchange. As a
result, the exchanges EX1, EX2 (FIG. 1) need not reassemble the ATM
cells into an IP packet and are capable of deciding the transfer
destination of the cell stream (the overall IP packet) at the stage
at which the leading cell C.sub.0 is received. More specifically,
each exchange refers to the destination terminal address indicated
by the leading cell C.sub.0, assigns the prescribed datagram VCC
for the purpose of connectionless communication and thenceforth
transmits, via this datagram VCC, the data cells
C.sub.1.about.C.sub.n having line identifiers identical with those
of the leading cell C.sub.0.
Further, with the connectionless communication method of the
present invention, a plurality of datagram VCCs are provided
beforehand between the exchanges EX1 and EX2 and one of these
datagram VCCs is assigned to a respective one of connectionless
communication operations. This makes it possible to perform
connectionless communication that furnishes the bandwidth and QOS
requested by a terminal through use of the leading cell. Thus, in
accordance with the connectionless communication method of the
present invention, cut-through is achieved by a special-purpose
datagram VCC from the initial change of communication.
(b) Change to Optimum Route
With the conventional IP switch approach, the opportunity to use
cut-through at an ATM switch unit is when a terminal has sent an
RSVP packet, as shown in FIG. 38. There are three reasons for this.
Specifically, (1) a large quantity of data generally does not flow
at the initial stage of communication. (2) A constant bit-rate
(CBR) application requiring the assurance of a necessary bandwidth
and QOS usually is started up in the second stage of communication.
(3) The terminal is incapable of correctly ascertaining the
necessary bandwidth, QOS and persistence of communication at the
initial stage, which is when the aforementioned CBR applications
have not yet been started up.
If this approach were to be applied to the connectionless
communication method of the present invention, information such as
the necessary bandwidth and QOS entered in the leading cell C.sub.0
of the present invention would be inaccurate.
Accordingly, the connectionless communication method of the present
invention is so adapted that when information such as the necessary
bandwidth and QOS has changed, the terminal sends the exchange a
datagram cell (the aforesaid request-change cell) that is for
changing the request, whereby the exchange is notified of the
latest request. Upon receiving the request-change cell, the
exchange, rather than executing routing processing, raises the set
bandwidth and QOS of the already assigned datagram VCC to the
necessary bandwidth and QOS that have been requested. In a case
where the physical line in which the already assigned datagram VCC
resides cannot assure the necessary bandwidth and QOS, the network
management center responds to a request from the exchange
accommodating the originating terminal by establishing a direct VCC
between end-to-end terminals and providing this VCC to the terminal
as a new route.
The method of assuring the route to the destination terminal is the
same as that for establishing the VCC of connection-oriented
communication in an ordinary ATM exchange network. Thus, in a case
where a terminal requests connectionless communication, the present
invention, while assuring the initial stage of communication with
the datagram approach, establishes in the meantime a datagram VCC,
which meets the requirements of the terminal, between end-to-end
terminals and supplies this VCC to the terminal.
(C) Embodiment
(a) Network Configuration
FIG. 3 is a diagram showing the configuration of a network which
performs connectionless communication according to the present
invention. The network includes terminals A.about.D and ATM
exchanges EX1.about.EX4. Further, VCC1 is a datagram VCC between
the terminal A and the exchange EX1, VCC2 a datagram VCC between
the terminal B and the exchange EX1, VCC3.about.VCC5 datagram VCCs
between the exchanges EX1 and EX2, VCC6.about.VCC8 datagram VCCs
between the exchanges EX2 and EX3, VCC9.about.VCC11 datagram VCCs
between the exchanges EX3 and EX4, VCC12 a datagram VCC between the
terminal C and the exchange EX4, and VCC13 a datagram VCC between
the terminal D and the exchange EX4. The datagram VCCs
(VCC1.about.VCC13) are set up between the terminals and ATM
exchanges and between mutually adjacent ATM exchanges beforehand in
such a manner that cells can be transferred from a prescribed
originating terminal to the terminal of another party.
Establishing a datagram VCC in advance is performed in the same
manner as in the prior-art datagram method. However, a
characterizing feature of the present invention is that a plurality
of datagram VCCs are established beforehand in parallel. That is,
whereas a plurality of communication operations share a single
common datagram VCC in the prior art, the connectionless
communication approach of the present invention sets up a plurality
of parallel datagram VCCs, thereby making it possible to assign a
datagram VCC exclusively for each individual communication.
(b) Construction of ATM Terminal
FIG. 4 is a diagram showing the construction of an ATM terminal.
The ATM terminal architecture includes a higher layer application
11, a higher layer communication protocol controller 12, an ATM
communication controller 13 and an ATM line interface 14. The ATM
communication controller 13 has a VCC controller 13a and a data
transfer controller 13b. The VCC controller 13a is provided with a
datagram cell generator 13c.
In connection-oriented communication, the higher layer
communication protocol controller 12 of the originating terminal
(assumed to be terminal A) delivers information (destination
terminal address, necessary bandwidth, QOS, etc.) for connection
set-up to the VCC controller 13a before communication starts, as
described earlier with reference to FIG. 32. As a result, the VCC
controller 13a, via the exchange EX1 and through use of a common
signal line (a signaling VCC), requests the network management
center (not shown) to establish a connection. In response to the
request from the originating terminal A, the network management
center sets up a route to the other party's terminal (assumed to be
terminal B) and instructs each exchange along the route to
establish a VCC. The ATM exchange EX1 notifies the originating
terminal A and the ATM exchange EX4 notifies the terminal C on the
terminating side of the line identifiers VPI/VCI used in
communication. The data transfer controller 13b thenceforth accepts
the transferred data from the higher layer, disassembles this data
into cells, attaches the line identifiers (VPI/VCI) of which it has
been notified to the cells and then sends the cells to the line.
Each of the exchanges EX1.about.EX4 switches and transmits the
cells while changing the line identifiers of the input cells. The
terminal C accepts cells, which have the specified line
identifiers, transmitted from the exchange EX4 and assembles the
cells into data.
The higher layer protocol 12 delivers the information such as the
destination terminal address, necessary bandwidth and QOS to the
VCC controller 13a in connectionless communication as well.
However, in the case of connectionless communication, the datagram
cell generator 13c of the VCC controller 13a generates the datagram
cell (leading cell) shown in FIG. 2 and (1) attaches the line
identifiers (VPI/VCI), which have been set beforehand for the
datagram VCC (VCC1) between the terminal and the exchange, to the
cell header of this leading cell, and (2) includes the cell
identifier ID, destination terminal address DA, originating
terminal (source terminal) address SA and other information in the
payload of the cell and then sends the cell to the line. Next, the
data transfer controller 13b accepts the transferred data from the
higher layer, disassembles this data into cells, attaches line
identifiers (VPI/VCI), which are identical with those that were
added onto the leading cell, to these cells and then sends the
cells to the line. Each of the exchanges EX1.about.EX4 refers to
the destination terminal address indicated by the leading cell,
assigns a prescribed datagram VCC for the purpose of connectionless
communication and, using the above-mentioned datagram VCC,
transmits data cells having line identifiers identical with those
of the leading cell. The terminal C accepts the cells transmitted
from the exchange EX4 and assembles them into data.
It should be noted that the cell identifier ID in the leading cell
is a 2-byte bit string indicating that the cell is a datagram cell.
The destination terminal address AD is the IP address of the
terminal on the terminating side or a subscriber number used by a
B-ISDN, the source terminal address SA is the IP address of the
originating terminal or a subscriber number used by the B-ISDN, and
the other information is the protocol identifier, traffic
descriptor, QOS class, communication persistence, etc.
The protocol identifier indicates the particular protocol address
specified by the terminal address described in the address field,
and the traffic descriptor indicates such properties as average
speed, peak speed, burstiness and peak maintenance time. This
traffic descriptor is the same as that used in a signaling cell at
the time of call set-up in a B-ISDN. QOS (Quality of Service) class
indicates, in the form of categories, quality stipulated by cell
loss rate, delay time, delay fluctuation, etc. QOS class is the
same as that used in the signaling cell of a B-ISDN. Communication
persistence is duration of communication calculated from, say, a
prediction of the total quantity of data exchanged by an
application.
Thus, the leading cell possesses a unique bit string, which
indicates that the cell is a datagram cell (leading cell), in the
two bytes that follow the cell header. This makes it possible for
an exchange to detect leading cells that arrive at an arbitrary
timing. Further, in connectionless communication, a terminal
address used to route data is not limited to an IP address; the
subscriber number in a B-ISDN may be used as well. That is, the
higher layer protocol is not limited to a TCP/IP. This means that
the protocol identifier is provided in the information field F4 of
the leading cell. As a result, each exchange that has received a
leading cell is capable of determining which protocol address is
indicated by the terminal address.
(c) Construction of Exchange
FIG. 5 is a diagram showing the construction of the exchange EX1.
The other exchanges EX2.about.EX4 are identically constructed. The
exchange EX1 includes an ATM switch unit 21 and a datagram VCC
assignment unit 22. The ATM switch unit 21 has an ATM switch 21a
that switches cells to a prescribed path, discriminates datagram
cells (leading cells) and sends the cells to the datagram VCC
assignment unit 22, and a switching table 21b for storing
correspondence between line identifiers (VPI/VCIs) of input VCCs
and line identifiers (VPI/VCIs) of output VCCs. The ATM switch 21a
sends input cells to prescribed output VCCs upon referring to the
corresponding relationships that have been stored in the switching
table 21b.
The datagram VCC assignment unit 22 has a datagram cell reader 22a
for reading and outputting information included in the payload of a
datagram cell, and a routing table 22b storing the correspondence
between terminal addresses and switching destinations (exchanges).
Since the switching destination is exchange 2 if the destination
terminals are C and D, "Exchange 2" is stored in the table in
correspondence with the terminal addresses of the terminals C and D
in the manner illustrated. The datagram VCC assignment unit 22
further includes a VCC table 22c for managing, in regard to each
datagram VCC set in advance between the table's own exchange
(exchange 1) and another exchange, the set QOS class, the set
bandwidth, whether the datagram VCC is in use or not, the QOS
required by connectionless communication, the necessary bandwidth,
communication persistence, the source address and the destination
address, etc. It should be noted that only the VCC table of the
datagram VCCs established between the exchanges EX1 and EX2 is
illustrated in FIG. 5. The datagram VCC assignment unit 22 further
includes a routing controller 22d for deciding a prescribed
datagram VCC by referring to the routing table 22b and VCC table
22c based upon the destination address indicated by the leading
cell, and for storing, in the switching table 21b, the
correspondence between the line identifiers of the leading cell and
the line identifiers of the datagram VCC. More specifically, the
routing controller 22d obtains the exchange EX2, which is the
switching destination, from the routing table 22b based upon the
destination terminal address indicated by the leading cell, and
then refers to the VCC table 22c on the basis of the necessary band
and necessary QOS, which are included in the leading cell, to
decide the prescribed datagram VCC that has been set beforehand
between the exchanges EX1 and EX2.
A summary of the operation of the exchange is as follows: (1) The
ATM switch 21a performs switching in the ATM layer by constantly
searching the switching table 21b on the basis of the line
identifiers attached to the input cells. (2) Upon receiving a
datagram cell (the leading cell), the datagram cell reader 22a
reads the various information contained in the payload of the
leading cell and delivers this information to the routing
controller 22d. (3) The routing controller 22d scrutinizes the
destination terminal address field of this cell, searches the
routing table 22b and VCC table 22c to decide the
output-destination datagram VCC assigned to this communication, and
registers this datagram VCC in the switching table 21b. Data cells
having line identifiers identical with those of the leading cell
are thenceforth transmitted to the datagram VCC that has been
decided.
Thus, time-consuming assembling of a packet is unnecessary.
Further, it suffices to execute the processing of steps (2) and (3)
merely upon receiving the leading cell; subsequent cells are routed
to the prescribed path at high speed merely by the processing of
step (1).
(d) Detailed Operation of Exchange
Reference will be had to the flowchart of FIG. 7 to describe the
operation of the exchange EX1 in regard to a case where the
terminal A has sent data addressed to the terminal C to a datagram
VCC (VCC1) in a network in which datagram VCCs (VCC1.about.VCC13)
having the QOS classes shown in FIG. 6 and a bandwidth of 1.5 MHz
have been established beforehand between terminals and exchanges
and between mutually adjacent exchanges.
First, the ATM switch 21a of the exchange 1 detects the datagram
cell (the leading cell) and inputs the cell to the datagram cell
reader 22a (step 101). The datagram cell reader 22a reads the
destination terminal address from the destination terminal address
field F2 in the payload of the leading cell and verifies that this
address is "address C" (step 102). Next, the routing controller 22d
searches the routing table 22b based upon the verified terminal
address C and confirms that the switching destination is the
exchange 2 (step 103).
Next, the routing controller 22d verifies the QOS class from the
field F4 of the datagram cell (the leading cell) (step 104). Here
it is assumed that the QOS class requested by the leading cell is
"QOS=1". The routing controller 22d then searches the VCC table 22c
addressed to the exchange 2 (step 105) and assigns VCC3 as the
optimum datagram VCC that satisfies the requested QOS class (step
106). If a datagram VCC of a QOS class that matches the QOS class
requested by the datagram cell has not been registered in the VCC
table 22c, or if this datagram VCC is currently in use, a datagram
VCC having a class better than the requested QOS class is assigned
to the extent possible (Class 1 is the best class and Class 5 is
the worst class).
When the assignment of the datagram VCC is completed, the routing
controller 22d updates the VCC table 22c (step 107) and stores the
correspondence between the line identifiers (VPI/VCI) of the
leading cell and the line identifiers (VPI/VCI) of the assigned
datagram VCC in the switching table 21b (step 108). The VCC table
22c is updated from the content shown in FIG. 5 to the content
shown in FIG. 8A by the processing of step 107. Further, the
corresponding relationship between the line identifiers of VCC1 and
VCC3 is stored in the switching table 21b by the processing of step
108 in the manner shown in FIG. 8B.
The exchange EX1 thenceforth transfers the datagram cell (the
leading cell) addressed to terminal C to the datagram VCC (VCC3)
(step 109). Upon receiving the leading cell address to terminal C,
the exchange EX2 assigns VCC6 to this communication as the datagram
VCC through a procedure similar to that described above. Similarly,
the exchange EX3 assigns VCC9 to this communication as the datagram
VCC, and the exchange EX4 assigns VCC12 as the datagram VCC,
thereby establishing a connectionless communication path between
the terminals A and C.
The ATM switch 21a of each of the exchanges EX1.about.EX4
thenceforth refers to the switching table 21b to transmit data
cells having line identifiers identical with those of the leading
cell to the assigned datagram VCC that is the destination of the
output.
The fact that the necessary bandwidth is 3M in FIG. 8A indicates
that the necessary bandwidth specified by the traffic descriptor in
the datagram cell (the leading cell) was 3M. Similarly, the fact
that persistence is 1 indicates that the value specified by the
communication persistence in the datagram cell was 1. This
communication persistence data is obtained by standardizing
communication durations to 1.about.n. Time may also be used as the
communication persistence data.
(e) Exchange Having Allocated Bandwidth Optimizing Function
(e-1) Construction
FIG. 9 is a diagram showing the construction of an exchange
equipped with a function for optimizing allocated bandwidth.
Components identical with those of the exchange shown in FIG. 5 are
designated by like reference characters. This exchanges differs
from that of FIG. 5 in that the datagram VCC assignment unit 22 is
provided with a bandwidth table 22e and a VCC table management unit
22f. The bandwidth table 22e stores, for every physical line
connected to the exchange, the correspondence among (1) the
physical bandwidth (maximum usable bandwidth) of the line, (2) the
bandwidth currently in use, and (3) the remaining bandwidth capable
of being allocated. The VCC table management unit 22f performs
bandwidth allocation optimization control based upon the content of
the bandwidth table 22e and the band (necessary band) and QOS class
requested by the originating terminal.
(e-2) First Bandwidth Reallocation Control
In the control operation of FIG. 7, the exchange EX1 assigns a
1.5-Mbps datagram VCC (VCC3) to the datagram cell (leading cell) of
connectionless communication between the terminals A and C
requesting 3 Mbps and the content of the VCC table 22c is as shown
in FIG. 8A. The reason for this is that not a very large bandwidth
can be allocated to an unused datagram VCC set beforehand for each
exchange. In the case of exchange EX1, 1.5 Mbps is allocated to
each VCC. Thus, there are many cases in which a datagram VCC having
a bandwidth that does not satisfy the bandwidth required by the
datagram cell (the leading cell) must be allocated.
Accordingly, the exchange of FIG. 9 performs control in such a
manner that the already available 1.5-Mbps datagram VCC is supplied
for the connectionless communication requested and, while
communication is being supported at this bandwidth, the allocated
bandwidth of this datagram VCC is increased up to the bandwidth
requested by the datagram cell (the leading cell). As a result of
such control, communication can continue smoothly. In the event
that the line to the exchange of the next stage does not possess
sufficient bandwidth resources for increasing the bandwidth in this
case, the allocated bandwidths of other unused datagram VCCs are
reduced to acquire allocated bandwidth resources for the sake of
the above-mentioned datagram VCC currently in use. Similarly, in a
case where there has been a change in the necessary QOS, control is
performed so as to maintain communication at the originally
allocated QOS class and change the QOS class of the datagram VCC in
the meantime.
FIG. 10 is a flowchart of processing for first allocation
optimization control by the VCC table management unit 22f.
A datagram VCC having the prescribed QOS is assigned to
connectionless communication requested by the leading cell (step
121). As a result, the content of the VCC table 22c becomes as
shown in FIG. 11A.
Next, the VCC table management unit 22f obtains the set bandwidth
F.sub.S of the assigned datagram VCC from the VCC table 22c and
compares the set bandwidth F.sub.S and the requested necessary
bandwidth F.sub.R in terms of the magnitudes thereof (step 122). If
F.sub.S.gtoreq.F.sub.R holds, reallocation of bandwidth is not
carried out and the end of connectionless communication is awaited
(step 123). In response to end of communication, the assigned
datagram VCC is released and the various tables are updated (step
124).
If F.sub.S <F.sub.R is found to hold at step 122, however, then
the VCC table management unit 22f refers to the bandwidth table 22e
and determines whether the physical line in which the datagram VCC
exists has enough surplus bandwidth to increase the set bandwidth
(step 125). If there is enough surplus bandwidth to increase the
set bandwidth to the necessary bandwidth, then the VCC table
management unit 22f raises the set bandwidth F.sub.S to the
necessary bandwidth F.sub.R and updates the content of the VCC
table 22c and bandwidth table 22e (step 126). As a result, the
content of the VCC table 22c is updated from the content shown in
FIG. 11A to the content shown in FIG. 11B. The end of
connectionless communication is then awaited (step 123). In
response to end of communication, the assigned datagram VCC is
released and the various tables 22c, 22e, etc., are updated (step
124).
If it is found at step 125 that surplus bandwidth does not exist,
then the VCC table management unit 22f refers to the VCC table 22c
and judges whether it is possible to reduce the allocated
bandwidths (set bandwidths) of other unused datagram VCCs (step
127). If this is possible, then the VCC table management unit 22f
reduces the allocated bandwidths of these other unused datagram
VCCs and updates the content of the VCC table 22c and bandwidth
table 22e (step 128). As a result, the content of the VCC table 22c
is updated from the content shown in FIG. 11A to the content shown
in FIG. 11C. The end of connectionless communication is then
awaited (step 123). In response to end of communication, the
assigned datagram VCC is released and the various tables 22c, 22e,
etc., are updated (step 124). In a case where the set bandwidth
F.sub.S cannot be increased to the necessary bandwidth F.sub.R even
when the allocated bandwidths (set bandwidths) of other unused
datagram VCCs are reduced at step 127, control is performed in such
a manner that communication satisfying the necessary bandwidth can
be carried out by other means, e.g., by establishing a direct VCC,
described later.
(e-3) First Bandwidth Reallocation Control
During the time that connectionless communication is being
maintained via a datagram VCC, an application which generates the
transfer of a large quantity of data may be started up at a
terminal and the particulars (necessary QOS, necessary bandwidth,
communication persistence, etc.) which the terminal requests of the
network may change. In such case the ATM terminal sends a datagram
cell (request-change cell) in order to notify of the requested
change, thereby informing the network of the change in request. The
network performs bandwidth and QOS reallocation control so as to
satisfy the request. It should be noted that the request-change
cell has a structure exactly the same as that of the leading
cell.
FIG. 12 is a diagram useful in describing the operation of an ATM
terminal when a request is changed. The higher layer communication
protocol controller 12 of the ATM terminal notifies the VCC
controller 13a of a change in bandwidth, necessary QOS and total
quantity of data required for execution of an application. In
response, the datagram cell generator 13c of the VCC controller 13a
generates a datagram cell (request-change cell) having a format
identical with that of the leading cell shown in FIG. 2 and sends
the generated cell to the datagram VCC. The exchange that has
detected the datagram cell (request-change cell) searches the
switching table 21b and determines whether the datagram VCC on
which the cell arrived has already been registered, thereby
discriminating whether the datagram cell is a leading cell or
request-change cell. That is, if the datagram VCC has not been
registered, then the arriving cell is the leading cell. If the
datagram VCC has been registered, on the other hand, then the
arriving cell is the request-change cell. If the arriving cell is
the request-change cell, then the datagram VCC has already been
assigned, switching processing is not executed again and control
for reallocating bandwidth and QOS is carried out so as to satisfy
the new request.
FIG. 13 is a flowchart of control performed by an exchange when a
request is changed.
If a datagram cell is received (step 101), the exchange searches
the switching table 21b (step 201) and determines whether a
datagram VCC on which the cell arrived has already been registered
(step 202). If the datagram VCC on which the cell arrived has not
been registered in the switching table 21b, this means that the
arriving cell is the leading cell and, hence, the control (steps
102.about.109) described above with reference FIG. 7 is
executed.
If it is found at step 202 that the datagram VCC on which the cell
arrived has been registered in the switching table 21b, on the
other hand, then the cell is the request-change cell. Accordingly,
the exchange updates the necessary bandwidth, necessary QOS and
communication persistence in the VCC table 22c based upon the
request indicated by the request-change cell (step 203). The
exchange then executes bandwidth and QOS optimization processing so
as to satisfy the new request (step 204).
FIG. 14 is a flowchart of optimization processing executed by an
exchange. First, the exchange refers to the VCC table 22c and
compares the set bandwidth F.sub.S and the requested necessary
bandwidth F.sub.R in terms of the magnitudes thereof (step 205a).
If F.sub.S.gtoreq.F.sub.R holds, then the program proceeds to QOS
reallocation processing. If F.sub.S <F.sub.R holds, however,
then the exchange refers to the VCC table 22c and determines
whether the shortfall (=F.sub.R -F.sub.S) is capable of being
appropriated from the allocated bandwidths (set bandwidths) of
other unused datagram VCCs (step 205b). If this is possible, then
the exchange reduces the allocated bandwidths of these other unused
datagram VCCs to make up for the shortfall (step 205c). However, if
it is impossible for the shortfall to be appropriated from the
allocated (set) bandwidths of other unused datagram VCCs, then
establishment of a direct VCC is requested. The establishment of a
direct VCC will be described later.
When processing for reallocating bandwidth ends, the exchange
refers to the VCC table 22c and compares the set QOS (=Q.sub.S) and
the necessary QOS (=Q.sub.R) (step 205d). Optimization processing
is terminated if Q.sub.S =Q.sub.R holds. If Q.sub.S.noteq.Q.sub.R
holds, however, the exchange determines whether the set QOS is
capable of being changed to the necessary QOS (step 205e). If the
change is possible, then the exchange changes the set QOS to the
necessary QOS and terminates optimization processing (step 205f).
If the change is not possible, however, then the exchange requests
establishment of a direct VCC.
(f) Communication Termination Control
When connectionless communication carried out using a datagram VCC
ends, the datagram cell generator 13c of the ATM terminal generates
a datagram cell (communication-end notification cell), which
indicates that communication using the above-mentioned datagram VCC
has ended, and sends the cell to the exchange. The exchange
executes termination processing upon receiving the
communication-end notification cell.
FIG. 15A is a diagram useful in describing the operation of the ATM
terminal when communication ends. The higher layer communication
protocol controller 12 of the ATM terminal responds to the end of
communication by notifying the VCC controller 13a of this fact. As
a result, the datagram cell generator 13c of the VCC controller 13a
generates a datagram cell (communication-end notification cell),
shown in FIG. 15B, for giving notification of the end of
communication, and sends this cell to the datagram VCC. The
datagram cell generator 13c inserts invalid data, which is composed
of all 0s, in the information field F4 of the communication-end
notification cell to make this call distinguishable from other
datagram cells.
FIG. 16 is a flowchart of communication termination processing
executed by an exchange. When a datagram cell is received (step
101), the exchange searches the switching table 21b (step 201) and
determines whether the datagram VCC on which the cell arrived has
already been registered (step 202). If the datagram VCC on which
the cell arrived has not been registered in the switching table
21b, this means that the arriving cell is the leading cell and,
hence, the control (steps 102.about.109) described above with
reference FIG. 7 is executed.
If it is found at step 202 that the datagram VCC on which the cell
arrived has been registered in the switching table 21b, on the
other hand, then the exchange refers to the F4 field of this cell
to determine whether the content of this field is all 0s (steps
301, 302). If the content of this field is not all 0s, this means
that the arriving cell is the request-change cell. Accordingly, the
exchange updates the necessary bandwidth, necessary QOS and
communication persistence in the VCC table 22c based upon the
request indicated by the request-change cell (step 203). The
exchange then executes bandwidth and QOS optimization processing so
as to satisfy the new request (step 204).
If it is found at step 302 that the content of this field is all
0s, this means that the arriving cell is the communication-end
notification cell. Accordingly, the exchange updates the content of
the VCC table 22c. That is, the exchange clears the data conforming
to the datagram VCC used thus far (step 303) and updates the
content of the switching table 21b. More specifically, the
correspondence between the line identifiers of the input datagram
VCC used thus far and the line identifiers of the output datagram
VCC is deleted from the switching table 21b by the exchange (step
304). Thus, owing to the fact that a terminal sends a datagram cell
indicative of the end of communication, the exchange is released
from assigning a datagram VCC to this communication at the end of
communication, whereby it is possible to avoid using more network
resources than necessary. Further, the exchange sends the
communication-end notification cell to the next terminal along the
route (step 305). As a result, other terminals are similarly
released from assigning datagram VCCs and, as a consequence, the
route between the terminals A and C established by datagram
vanishes.
By virtue of the above-described communication termination
processing, the VCC table 22c and switching table 21b are cleared
to their original states, as shown in FIGS. 17A and 17B,
respectively.
(g) Control for Establishment of Direct VCC Between Terminals
(g-1) Necessity for Direct VCC
When an ATM terminal has sent a request-change cell to request the
network for increased bandwidth, there are cases where the network
will be incapable of assuring a bandwidth that satisfies the
request with a route that has already been established in such
cases the exchange regards the request-change notification from the
terminal as a request to establish connection-oriented
communication and requests the network management center to
establish a direct VCC between terminals. The bandwidth necessary
for continuation of communication is acquired by performing
communication via the VCC established by the network management
center.
(g-2) Network Configuration
FIG. 18 is a diagram showing the configuration of a network that
makes possible control for establishing a direct VCC between
terminals. Shown in FIG. 18 are ATM terminals A D, ATM exchanges
EX1.about.EX4, a network NWK composed of a group of ATM exchanges,
and a network management center NMC.
A connectionless communication route (exchanges
EX1.fwdarw.EX2.fwdarw.EX3.fwdarw.EX4) is established between the
terminals A and C, which proceed to communicate via this route.
Assume that the terminal A has sent a request-change cell
requesting a bandwidth of 30 Mbps. Since the maximum usable
bandwidth over a line between the exchanges EX1 and EX2 is 25 Mbps,
the bandwidth of 30 Mbps necessary for connectionless communication
between the terminals A and C cannot be acquired over the already
established communication path. In such case the exchange EX1, on
the basis of request-change notification from the terminal A,
requests the network management center NMC to establish a direct
VCC between the terminals A and C using the common signal line. In
connection-oriented communication (see FIG. 32), a request of this
kind directed to the network management center usually is issued by
the VCC controller of the ATM terminal. However, when a direct VCC,
which is substituted for a route already established by
datagram-type communication (connectionless communication), is
established, the exchange EX1, not the ATM terminal, sends the
network management center NMC the request to establish the direct
VCC.
(g-3) Construction of Exchange
FIG. 19 is a diagram showing the construction of an exchange which
implements control for requesting a direct VCC. Components
identical with those of the exchange shown in FIG. 9 are designated
by like reference characters. This exchanges differs from that of
FIG. 9 in the provision of a VCC establishing agent 23. On the
basis of the content of the VCC table 22c, the VCC establishing
agent 23 generates signaling data and sends the network management
center NMC a request to establish a direct VCC between the
terminals A and C. More specifically, the VCC establishing agent 23
(1) monitors the requested terminal bandwidth F.sub.R that has been
registered in the VCC table 22c and the remaining line bandwidth
managed by the bandwidth table 22e. If the requested bandwidth of
the terminal can be furnished by the remaining bandwidth of the
line, the VCC establishing agent 23 performs control in such a
manner that the remaining bandwidth of the line is allocated to the
datagram VCC. (2) If the requested bandwidth of the terminal cannot
be supplied by the remaining bandwidth of the line, then the VCC
establishing agent 23 generates data for requesting the network
management center NMC to establish a direct VCC. (3) The VCC
establishing agent 23 uses the common signal line to send the
network management center NMC signaling data which requests
establishment of the direct VCC between the terminals.
(g-4) Communication Control Based Upon Establishment of Direct
VCC
FIG. 20 is a flowchart of direct VCC establishment and
communication control.
Upon being notified of an increase in necessary bandwidth by a
datagram cell (request-change cell), i.e., upon detecting an
increase in necessary bandwidth by referring to the VCC table 22c
(step 401), the VCC establishing agent 23 determines whether the
line has enough surplus bandwidth to increase the set bandwidth
F.sub.S of the datagram VCC assigned to connectionless
communication to the requested bandwidth F.sub.R (step 402). If
enough bandwidth remains, the VCC establishing agent 23 increases
the set bandwidth F.sub.S to the requested bandwidth F.sub.R (step
403).
If the line does not have enough surplus bandwidth to increase the
set bandwidth F.sub.S to the requested bandwidth F.sub.R, on the
other hand, the VCC establishing agent 23 refers to the VCC table
22c to obtain the necessary bandwidth, necessary QOS, source
address and destination address, uses this information to generate
signaling data for requesting establishment of a direct VCC (step
404), and uses the common signal line to request the network
management center NMC to establish the direct VCC between the
terminals A and C (step 405).
Upon receiving the request to establish the direct VCC between the
terminals A and C, the network management center NMC calculates a
route between the terminals A and C, instructs each exchange in the
group of ATM exchanges constituting the route to set a VCC between
the terminals A and C, thereby establishing a direct VCC between
terminals A and C (step 406). Next, the network management center
NMC notifies the terminals A and C of the line identifiers
(VPI/VCI) of the direct VCC, which is substituted for the datagram
VCC (step 407), via the common signal line.
As a result, the VCC controller 13a of the terminal receives the
line identifiers of the direct VCC from the common signal line, as
shown in FIG. 21. Upon being notified of the line identifiers of
the direct VCC, the VCC controller 13a refers to the communication
information being managed by the datagram cell generator 13c and
recognizes that the direct VCC has been established for the sake of
communication that was being performed by the datagram VCC until
now. Next, the VCC controller 13a notifies the data transfer
controller 13b of the change in the output VCC and delivers the
line identifiers of the direct VCC. The data transfer controller
13b thenceforth forms data, which is received from a higher layer,
into cells and then sends the cells to an exchange upon attaching
the line identifiers of the direct VCC to the cell headers (step
408). Further, the datagram cell generator 13c cancels the
assignment of the above-mentioned datagram VCC that was being
managed and sends the exchange a datagram cell (the
communication-end notification cell), which gives notification of
the end of communication based upon the above-mentioned datagram
VCC (step 409) As a result, the datagram VCC (within the network)
that had been assigned to connectionless communication is restored
to the not-in-use state, after which it becomes possible for this
datagram VCC to be used for communication between other terminals
(step 410).
(g-5) Direct VCC Establishment and Communication Control Based Upon
Increase in Communication Persistence
The foregoing is for a case where an ATM terminal has caused as
increase in requested bandwidth in the network. However, there is
also a case where communication persistence (duration of
communication) increases owing to an increase in the quantity of
transmitted data. In such case also control can be performed so as
to carry out communication by establishing a direct VCC.
FIG. 22 is a flowchart of communication control in a case where
communication persistence (duration of communication) is
increased.
Upon being notified of an increase in communication persistence by
a datagram cell (request-change cell), i.e., upon detecting an
increase in communication persistence (duration of communication)
by referring to the VCC table 22c (step 501), the VCC establishing
agent 23 compares the duration of communication with a preset
threshold value (step 502) and terminates communication if the
duration is less than the threshold value. If the duration of
communication is equal to or greater than the threshold value,
however, then the VCC establishing agent 23 executes processing
identical with that of steps 404.about.410 of FIG. 20 and performs
communication control based upon a direct VCC. As a result,
communication which continues of an extended period of time can be
performed by the direct VCC and it is possible to prevent a
deficiency in standby datagram VCCs.
(g-6) Control for Requesting Establishment of VCC
If bandwidth cannot be assured by the datagram VCC (VCC3) between
the exchanges EX1 and EX2, then, in accordance with the
above-described control for establishing a direct VCC (see FIG.
18), the exchange EX1 sends the network management center NMC a
request to establish the direct VCC between the terminals A and C.
However, in a case where bandwidth cannot be assured also with the
lines between the exchanges EX2 and EX3 and between the exchanges
EX3 and EX4, a problem which arises is that the exchanges EX2 and
EX3 also issue requests for direct establishment of a direct VCC
between the terminals A and C simultaneously.
According, it is so arranged that if the exchanges EX2.about.EX4,
which do not directly accommodate the originating terminal, cannot
acquire bandwidth, then a request to establish a direct VCC is not
sent to the network management center NMC. Rather, as shown in FIG.
23A, the exchanges EX2.about.EX4 send the exchange EX1, which
directly accommodates the originating terminal A, a datagram cell
(bandwidth deficiency notification cell) which notifies the
exchange EX1 of the fact that bandwidth cannot be assured. As shown
in FIG. 23B, the bandwidth deficiency notification cell is
distinguished from other cells by inserting a unique bit string,
which indicates insufficient bandwidth, in the F4 field of the cell
payload.
More specifically, the operation performed is as follows:
(1) The exchange EX2 managing a bandwidth deficiency 1 sends the
exchange EX1 a bandwidth deficiency notification cell to notify it
of the fact that bandwidth is insufficient.
(2) Upon receiving the datagram cell (the bandwidth deficiency
notification cell) from the exchange EX2 notifying of the bandwidth
shortfall, the exchange EX1 sends the network management center NMC
a request for establishing a direct VCC between the terminals A and
C.
(3) The exchange EX3 managing a bandwidth deficiency 2 also sends
the exchange EX1 a bandwidth deficiency notification cell to notify
it of the fact that bandwidth is insufficient . However, since the
request to establish the direct VCC between the terminals A and C
has already been sent at step (2) above, the exchange EX1 does not
take any action in response to the bandwidth deficiency
notification cell from the exchange EX3. Further, the exchange EX2,
which has received the bandwidth deficiency notification cell sent
from the exchange EX3 to notify of the bandwidth shortfall, does
not take any action because it does not directly accommodate the
originating terminal A.
If this expedient is adopted, the exchange that sends the network
management center NMC the request to establish the direct VCC can
be limited solely to the exchange EX1 directly accommodating the
originating terminal this makes it possible to avoid duplication of
direct VCC establishment requests.
FIG. 24 is a flowchart of processing, inclusive of processing to
request establishment of a VCC, executed by an exchange.
If a datagram cell having the prescribed cell identifier is
detected (step 101), the exchange searches the switching table 21b
(step 201) and determines whether a datagram VCC on which the cell
arrived has already been registered (step 202). If the datagram VCC
on which the cell arrived has not been registered in the switching
table 21b, this means that the arriving cell is the leading cell
and, hence, the control (steps 102.about.109) described above with
reference FIG. 7 is executed.
If it is found at step 202 that the datagram VCC on which the cell
arrived has been registered in the switching table 21b, on the
other hand, then the exchange refers to the F4 field of this cell
to determine whether the content of this field is all 0s (steps
301, 302). If the content of this field is all 0s, this means that
the arriving cell is the communication-end notification cell.
Accordingly, the exchange updates the VCC table 22c. More
specifically, the exchange clears the data conforming to the
datagram VCC used thus far (step 303) and updates the content of
the switching table 21b. That is, the correspondence between the
line identifiers of the input datagram VCC and the line identifiers
of the output datagram VCC is deleted from the switching table 21b
by the exchange (step 304). Further, the exchange sends the
communication-end notification cell to the next terminal along the
route.
If it is found at step 302 that the content of the F4 field is not
all 0s, this means that the arriving cell is the request-change
cell or bandwidth deficiency notification cell. Accordingly, the
exchange determines whether the content of the F4 field is the bit
string indicative of insufficient bandwidth (step 601). If the
content is not the bit string indicative of insufficient bandwidth,
then the cell is the request-change cell and the exchange therefore
updates the necessary bandwidth, necessary QOS and communication
persistence of the VCC table 22c based upon the request indicated
by the request-change cell. The exchange then executes bandwidth
and QOS optimization processing so as to satisfy the new request
(step 204).
If it is found at step 601 that the content of the F4 field is the
bit string indicative of the shortfall in bandwidth, this means
that the cell is the bandwidth deficiency notification cell.
Consequently, the exchange reads the source terminal address of the
bandwidth deficiency notification cell and determines whether it
itself is directly accommodating the terminal indicated by this
address (steps 602, 603). If the terminal is not one directly
accommodated, then the exchange ignores the bandwidth deficiency
notification cell (step 604). If the originating terminal is being
directly accommodated, on the other hand, then the exchange
executes the processing (VCC establishment control) from step 404
onward in FIG. 20 (step 605).
(h) Multicast Communication
When multicast communication is performed in a datagram network
based upon a one-to-one communication protocol such as the
conventional TCP/IP, a terminal must repeat the same communication
procedure a number of times equivalent to the number of
communication partners and must send data to each of these
partners. However, this increases the load upon the terminal
sending the information and the necessary bandwidth of the network
in proportion to the number of terminals of the other parties.
Accordingly, the present invention is such that when multicast
communication is performed, the terminal that is the source of a
transmission need only send the data one time regardless of the
number of communication partners. Moreover, according to the
present invention, data is copied at an exchange where the route
branches to each communication partner and the copied data is
transmitted to the terminals of this exchange. This lightens
terminal load and suppresses and constrains the necessary bandwidth
of the network.
FIGS. 25A and 25B are diagrams useful in describing such multicast
communication and illustrate a case in which data is multicast from
terminal A to terminals C, D via the exchanges EX1.about.EX4. FIG.
25A shows multicast communication according to the prior art and
FIG. 25B multicast communication according to the method of the
present invention. With conventional multicast communication,
terminal A must send the same data to terminals C and D, as
illustrated in FIG. 25A. By contrast, the method of the present
invention is such that if terminal A sends data only once, the
exchange EX4 will copy the data and transmit the copied data to
each of the terminals C and D. This lightens the load on the
originating terminal and constrains the necessary bandwidth of the
network.
In order to make the above-described multicast communication
according to the invention possible, the addresses of a plurality
of communicating partner terminals must be specified by the
datagram cell (the leading cell). Higher layer protocols include
protocols having group addresses for multicasting, as in the manner
of group IP addresses. If such a higher layer protocol is
available, all multicast communicating partner terminals can be
specified by a single address by describing a group address as the
group address of a group of communicating partner terminals of a
datagram cell.
However, in a case where data of a protocol not having a group
address is transmitted, only the addresses of the individual
terminals may be used. That is, only the address of one
communicating partner terminal can be specified by one datagram
cell (leading cell). Accordingly, in a case where multicast
communication is performed, the originating terminal that sends the
data sends datagram cells (leading cells) the number of which is
equivalent to the number of communicating partner terminals,
thereby designating the addresses of a plurality of communicating
partner terminals.
FIG. 26 is a diagram useful in describing control for specifying
the terminals of parties involved in multicast communication, FIGS.
27A, 27B and 27C are diagrams useful in describing the content of
switching tables of exchanges, and FIGS. 28A, 28B and 28C are
diagrams useful in describing the content of a VCC table of
datagram VCCs addressed from exchange EX1 to exchange EX2.
In a case where terminal A is to communicate with terminals C and D
by multicast communication, first terminal A sends the exchange EX1
a datagram cell (leading cell) addressed to terminal C.
(1) Upon receiving the leading cell addressed to terminal C, the
exchange EX1 judges that the switching destination is the exchange
EX2, assigns VCC3 as the datagram VCC and registers "VCC1-VCC3",
which indicates the correspondence between the input datagram VCC
and the output datagram VCC, in the switching table 21b (see FIG.
27A). In actuality, VCC1, VCC3 are specified by line identifiers
VPI/VCI, which have been set for these VCCs in advance. Further,
the exchange EX1 updates the VCC table 22c from the content shown
in FIG. 28A to the content shown in FIG. 28B by the assignment of
the datagram VCC. At this stage, however, the destination is still
the terminal C.
(2) Similarly, upon receiving the leading cell addressed to
terminal C, the exchange EX2 judges that the switching destination
is the exchange EX3, assigns VCC6 as the datagram VCC and registers
"VCC3-VCC6", which indicates the correspondence between the input
datagram VCC and the output datagram VCC, in the switching table
21b.
(3) Similarly, upon receiving the leading cell addressed to
terminal C, the exchange EX3 judges that the switching destination
is the exchange EX4, assigns VCC9 as the datagram VCC and registers
"VCC6-VCC9", which indicates the correspondence between the input
datagram VCC and the output datagram VCC, in the switching table
21b.
(4) Similarly, upon receiving the leading cell addressed to
terminal C, the exchange EX4 judges that the switching destination
is the terminal C, assigns VCC12 as the datagram VCC and registers
"VCC9-VCC12", which indicates the correspondence between the input
datagram VCC and the output datagram VCC, in the switching table
(see FIG. 27B).
Next, terminal A sends the exchange EX1 a leading cell addressed to
terminal D.
(5) Upon receiving the leading cell addressed to terminal D, the
exchange EX1 verifies that the switching destination is the
exchange EX2, which is no change from the previous switching
destination, and does not assign a datagram VCC anew. However, the
exchange EX1 enters terminal D in the destination field of the VCC
table 22c (see FIG. 28C). It should be noted that the set
bandwidths of VCC4 and VCC5 become 1.0 M and 0.5 M, respectively,
owing to bandwidth optimization processing.
(6) Similarly, upon receiving the leading cell addressed to
terminal D, the exchange EX2 verifies that the switching
destination is the exchange EX3, which is no different from the
previous switching destination, and does not assign a datagram VCC
anew.
(7) Similarly, upon receiving the leading cell addressed to
terminal D, the exchange EX3 verifies that the switching
destination is the exchange EX4, which is no different from the
previous switching destination, and does not assign a datagram VCC
anew.
(8) Upon receiving the leading cell of terminal D, the exchange EX4
verifies that the switching destination is terminal D, which
represents a change from the previous destination, newly assigns
VCC13 as the datagram VCC and adds "VCC9-VCC13" to the switching
table (see FIG. 27C).
Thus, an exchange that has received a leading cell from an input
datagram VCC that has been registered in the switching table 21b
newly assigns an output datagram VCC and adds it to the switching
table 21b only in a case where the switching destination has
changed. As a result, in the case of FIG. 26, the exchange 4 is
capable of copying the data and of transmitting the copied data to
each of the terminals C and D.
FIGS. 29 and 30 are flowcharts of control, inclusive of multicast
processing, performed by an exchange.
If a datagram cell having the prescribed cell identifier is
detected (step 101), the exchange searches the switching table 21b
(step 201) and determines whether a datagram VCC on which the cell
arrived has already been registered (step 202). If the datagram VCC
on which the cell arrived has not been registered in the switching
table 21b, this means that the arriving cell is the leading cell
and, hence, the control (steps 102.about.109) described above with
reference FIG. 7 is executed.
If it is found at step 202 that the datagram VCC on which the cell
arrived has already been registered in the switching table 21b, on
the other hand, then the exchange refers to the F4 field of this
cell to determine whether the content of this field is all 0s
(steps 301, 302). If the content of this field is all 0s, this
means that the arriving cell is the communication-end notification
cell. Accordingly, communication termination processing is executed
(steps 303, 304).
If it is found at step 302 that the content of the F4 field is not
all 0s, then the exchange determines whether the content of the F4
field agrees with the bit string indicative of insufficient
bandwidth (step 601). If the content of the F4 field is the bit
string indicative of insufficient bandwidth, then the exchange
executes VCC establishment control by the processing of steps 602
onward shown in FIG. 24 (step 610).
If it is found at step 601 that the content of the F4 field does
not agree with the bit string indicative of insufficient bandwidth,
then the exchange reads the destination terminal address contained
in the received cell, searches the routing table 22b based upon
this address and finds the exchange that is the switching
destination (steps 701, 702). The exchange thenceforth determines
the exchange that is the destination of switching from the
corresponding relationship between input VCC and output VCC
registered in the switching table 21b (step 703). The exchange then
checks to see whether the exchange that is the destination of
switching obtained at step S702 is contained in the exchange that
is the switching destination obtained at step S703. In other words,
the exchanges determines whether the switching destination is a new
switching destination (step 704).
If the switching destination is not a new switching destination,
this means that the received cell is the request-change cell and
therefore the exchange updates the necessary bandwidth, necessary
QOS and communication persistence of the VCC table 22c based upon
the request indicated by the request-change cell. The exchange then
executes bandwidth and QOS optimization processing so as to satisfy
the new request (step 204).
If the switching destination is a new switching destination, that
is, if the switching destination has changed, this means that the
received cell is a partner terminal notification cell for multicast
communication purposes. Accordingly, the terminal assigns a new VCC
as the datagram VCC (step 705), subsequently updates the content of
the VCC table (step 706) and stores the new VCC in the switching
table (step 707). The exchange then sends the cell to the newly
added datagram VCC.
Thus, in accordance with the present invention, a plurality of
datagram VCCs for connectionless communication for the purpose of
delivering data between exchanges are prepared in advance and
exclusive connections are supplied one at a time for individual
connectionless communications (datagram communications). As a
result, each individual terminal can be assured a bandwidth and
quality for the sending of data.
In accordance with the present invention, a connection-oriented
communication exchange, e.g., an ATM exchange, need not assemble
cells into an IP packet, thus making it possible to perform
connectionless communication utilizing fully the high-speed
switching characteristic of an ATM exchange.
In accordance with the present invention, a protocol identifier,
which identifies which protocol address is specified by a
destination terminal address, is included in a leading cell so that
an exchange is capable of identifying, by referring to the protocol
identifier, which protocol address is specified by the terminal
address indicated by the leading cell, As a result, not only the
Internet Protocol but various other higher layer protocols can be
supported.
In accordance with the present invention, data indicating bandwidth
or QOS class required for connectionless communication is included
in the leading cell, and an exchange is made to manage, by a VCC
table, in-use/not-in-use state of each datagram VCC and bandwidths
or QOS classes set for datagram VCCs. As a result, an exchange can,
by referring to the VCC table, readily assign a datagram VCC
satisfying the necessary bandwidth or QOS class indicated by the
leading cell.
In accordance with the present invention, communication can be
started even in a case where a datagram VCC that satisfies the
necessary bandwidth or QOS class requested by a terminal does not
exist. Moreover, communication that does satisfy the requirements
of the terminal can be performed after communication starts.
In accordance with the present invention, it is so arranged that if
a request-change cell has been received, the exchange, rather than
executing routing processing, executes only processing for altering
the set bandwidth of the already assigned datagram VCC to the
necessary bandwidth. As a result, the burden on the exchange is
alleviated because the exchange need not execute routing
processing. Moreover, communication that satisfies requirements
after a change can be performed.
In accordance with the present invention, it is so arranged that
when connectionless communication using a datagram VCC ends, the
terminal sends an exchange a communication-end notification cell
indicative of end of communication, and the exchange responds to
receipt of the communication-end notification cell by restoring the
assigned datagram VCC to the not-in-use state. As a result, a
datagram VCC can be utilized again for another connectionless
communication.
In accordance with the present invention, it is so arranged that if
a physical line does not have enough surplus bandwidth for
increasing the set bandwidth of a datagram VCC to a necessary
bandwidth when there has been a change in necessary bandwidth or
QOS class during the course of communication, a direct VCC between
terminals is established to perform communication. This makes
possible communication that positively satisfies requirements after
a change.
In accordance with the present invention, data indicating
communication persistence is included in the leading cell. If
communication persistence exceeds a predetermined threshold value,
a direct VCC between terminals is established to perform
communication. As a result, it is possible to prevent lack of
datagram VCCs in order to perform communication that continues over
an extended period of time.
In accordance with the present invention, an exchange which sends a
network management center a request to establish a direct VCC is
made the exchange directly accommodating the originating terminal.
As a result, only one exchange requests the network management
center to establish a direct VCC, thus making it possible to avoid
duplication of direct VCC establishment requests.
In accordance with the present invention, it is so arranged that
user cells are sent to a branch point via a common path, the user
cells are copied at the branch point and the copied cells are
distributed to a plurality of communication devices belonging to
other parties. In multicast communication, therefore, the load on
the originating terminal can be alleviated since this terminal need
only send the user cell stream one time. Moreover, an increase in
traffic can be suppressed.
As many apparently widely different embodiments of the present
invention can be made without departing from the spirit and scope
thereof, it is to be understood that the invention is not limited
to the specific embodiments thereof except as defined in the
appended claims.
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